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LCP, FCP, FP timing is not accurate #6672

Closed as not planned
Closed as not planned
@Dante-dan

Description

@Dante-dan

Is there an existing issue for this?

How do you use Sentry?

Self-hosted/on-premise

Which package are you using?

@sentry/vue

SDK Version

7.18.0

Framework Version

vue 3.2.45

Link to Sentry event

No response

Steps to Reproduce

  1. reload page
  2. find page load event
  3. the lcp fp fcp measurements are smaller than performance API

It looks like this is deliberately designed this way.. but in my opinionin, performance API provide startTimestamp meaning that from navigation Start to First Content Paint.

But normalizedValue ≈ FCP - new Date() is smaller than FCP, and it will be affected by javascript load time, specially in weak network.

This is fatal for performance optimization scenarios.

Expected Result

we should report startTimestamp to measurement's fcp/lcp/fp value, because it actual value.

Actual Result

normalizedValue ≈ FCP - new Date()

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